The invention relates to a multiple tube filter, consisting of at least one perforated filter element, wherein the outside of the filter element has spirally circulating grooves.
DE-OS 15 36 928 discloses a filter cartridge, as well as a filter element for use in this filter cartridge. The filter cartridge consists of a support sleeve made of plastic, which has been pushed into a tube-shaped filter sleeve of a felt material and is tightly enclosed by it. The support sleeve is perforated for the filtrate to run off. In one embodiment the support sleeve has a net-like appearance. To this end, two groups of rods bent into a spiral shape are arranged in such a way that their rises respectively extend in opposite directions. The rods are respectively connected with each other at their intersection points, which results in a net-like structure. The support sleeve is inserted into a tube-shaped filter sleeve of non-self-supporting needled felt, wherein the needled felt has such a high degree of inherent stiffness that the filter sleeve has a rigidity which is sufficient for maintaining its shape.
It is disadvantageous in respect to such a filter sleeve that a filter cake built upon the filter sleeve is not supported. There is therefore the danger that in the dried, shrunk state the filter cake collapses on itself. Then the flushing of the filter cake is only possible in a limited way, since the flushing liquid mainly runs off in the uncovered areas of the filter, while there is no flow through the filter cake, which lies in the lower area of the filter.